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# Hydraulic Single-Acting Valve Actuator

Single-acting hydraulic valve actuator

Valve Actuators

## Description

Use the Hydraulic Single-Acting Valve Actuator block as a pilot actuator for directional, pressure, or flow control valves in applications where all the forces, except spring force, and flow consumption can be neglected.

The actuator consists of a piston and a spring. The spring, which can be preloaded, tends to keep the piston at the initial position. As pressure applied to the piston develops enough force to overcome the spring preload, the piston moves to the opposite position until it reaches its maximum stroke.

The actuator is simulated according to the following equations:

where

 p Pressure applied to the piston s Piston displacement A Piston area F Instantaneous spring force Fpr Spring preload force Fmax Spring force at maximum piston displacement stroke Piston stroke or Actuator orientation with respect to the globally assigned positive direction. If pressure applied at port X moves the piston in positive direction, or equals 1. If pressure applied at port X moves the piston in negative direction, or equals –1.

Connection X is a hydraulic conserving port associated with the valve chamber. Connection P is a physical signal port whose output corresponds to piston displacement. Pressure applied at port X moves the piston in the positive or negative direction, depending on the value of the Actuator orientation parameter.

## Basic Assumptions and Limitations

• No loading, such as inertia, friction, hydraulic force, and so on, is taken into account. The only force considered is a spring force.

• No flow consumption associated with the piston motion, leakage, or fluid compressibility is taken into account.

## Dialog Box and Parameters

Piston area

Effective piston area. The default value is 2e-4 m^2.

Spring preload force. The default value is 20 N.

Full stroke force

Force necessary to move the piston to maximum stroke. The default value is 70 N.

Piston stroke

Piston stroke. The default value is 5e-3 m.

Actuator orientation

Specifies actuator orientation with respect to the globally assigned positive direction. The actuator can be installed in two different ways, depending upon whether it moves the piston in the positive or in the negative direction when pressure is applied at its inlet. If pressure applied at port X moves the piston in the negative direction, set the parameter to Acts in negative direction. The default value is Acts in positive direction.

## Ports

The block has the following ports:

X

Hydraulic conserving port associated with the valve chamber.

P

Physical signal port that outputs piston displacement.

## Examples

The following example shows a model of a pressure-relief valve built using the Hydraulic Single-Acting Valve Actuator and Orifice with Variable Area Round Holes blocks.